1. Field of the Invention
The invention relates to link chains, and in particular provides a link chain in which the connection between successive links is changeable between a rigid connection and a pivotable connection. The change can be made by displacing certain link plates against resilient bias so as to disengage them from adjacent links and permit pivoting. Preferably, this is accomplished by compressing certain links in the chain, which have laterally extending cam surfaces.
2. Prior Art
In a conventional elongated chain formed of connected links, each successive link in the chain has a body coupled by two link pins to the two adjacent links, namely the links that precede and follow the given link along the chain. Usually each link has two link plates that are laterally spaced relative to the longitudinal center line of the chain, although other chain structures are possible, such as links that alternate one and two plates, or successive links with any number of plates, etc. The link pins typically define parallel pivot axes.
An exemplary chain structure of such a description is the conventional roller chain. Each of the longitudinally connected serial links comprises two link plates that are laterally spaced by a bushing or roller. This bushing or roller engages in a rounded depression between teeth on the outer diameter of a sprocket or other similar structure for transmitting power using the chain. Some chains have flanges or tabs that protrude from certain of the link plates, providing a point at which attachments can be made to the chain.
A roller chain often has two different types of links. One type, which can be called a roller link, has two spaced hollow bushings extending between the lateral link plates. The other type, which can be called a pin link, has two spaced pivot pins, which usually are solid, extending between lateral link plates. Two successive roller links in the chain have a pin link that provides the structural connection between the roller links. The pivot pins of the pin link extend from one link plate of the pin link, through the hollow bushings of the roller plates, and attach to the other link plate of the pin link. Thus the pin links are laterally wider than the roller links, at least by a distance equal to the thickness of the link plates. The pin links are wider because their link plates straddle the outside surfaces of the roller links.
The roller chain is quite flexible, provided that the links remain in a plane that includes the longitudinal centerline of the chain. Within this plane, any two adjacent links can be relatively rotated around the common axis of the roller and the pin by which such adjacent links are connected to one another. As a limit, each of the links can be relatively rotated until it rotates forward or backward into contact with the next adjacent link.
There is a known type of chain that is structured to bend freely in one direction but not the other. In theory, such a chain is free to bend flexibly around two sprockets of an endless loop drive, but is not free to bend backwards, thus defining a flat and non-sagging bed between the sprockets for bearing weight. The links of such a chain are coupled by pivot pins located on the side of the chain facing the sprocket, at the longitudinal ends of typically block-shaped link bodies. When the chain is pivoted around a sprocket, abutting ends of the link bodies diverge. If one attempts a backward bend, the block shaped link bodies abut and the chain can only be bent “backwards” up to the point at which the links are in a straight line. An example of such a chain is disclosed in U.S. Pat. No. 5,970,701 Roden et al., which is hereby incorporated. A problem with such a chain is that a minor amount of play or looseness in the pivot pin joints due to manufacturing tolerances or other causes will permit the chain to sag. Similarly, if the abutting surfaces of the block-shaped links are individually too high or too low, the chain may be bumpy or may sag. As a result, it is often preferred to provide a rigid underlayment or track if a chain structure is to bear a load in the same plane that the chain is to flex.
In many uses for roller chains, the chain is closed in an endless loop that is of the length needed to pass around sprockets that are mounted at fixed rotation points on a chassis. One of the sprockets is usually coupled to driving power and the chain transmits the power to rotate another sprocket. The chain is relatively taut between the sprockets on one side of the endless loop, due to tension exerted by the driving sprocket. The chain is typically slack between the sprockets on the other side of the endless loop, but even so is in tension between the payout point on the drive sprocket and the take-up point on the driven sprocket, due to the force of gravity and sagging of the chain.
An arrangement with one driving sprocket and one driven sprocket is just an example. Chain arrangements can have any combination of powered sprockets and idlers. The chain may follow a path that bends only toward one side, or the path may bend sinuously forward and backward. In addition to transmitting rotational power, a chain can be used to move a device linearly along the chain path, e.g., back and forth between sprockets. However, chains that are structured for pivoting or relative rotation between links are typically useful only in tension. When not subjected to tension, or when in compression, the relatively-rotatable coupled links are free to pivot and cannot be relied upon for purposes of positioning or transfer of power.
In order to tension a chain or otherwise to support such an elongated flexible item, it is necessary to provide a support or chassis that is as long as the distance between the extremes of the path of the chain. In some instances, it is not practical to provide such a supporting structure.
Regardless of whether there is any slack or looseness in the pivot joints between links of a flexible chain, the chain must sag between horizontally spaced supported points. A tensioned flexible structure can only remain straight if it has no lateral load, or if an infinite amount of tension is applied, because sagging is a vector function related to lateral loading (e.g., vertical weight of a horizontally elongated structure) and tension. The chain acts like a suspension structure for the weight of the links (plus any load thereon), and sags in a parabolic arc that is a function of the relative forces of tension and gravity load.
A chain can be structured so as to bend in one direction as in the Roden patent mentioned above, or the chain can be supported on a linear track under a span between sprockets or other support points. It is possible to envision various support structures for such a track, including the possibility of a telescoping support track. These solutions have their own problems.
In the typical chain structure discussed above, the connected links alternate between roller links and pin links. It is also possible to have a chain in which the links are all identical, for example with each link having a pin end that is slightly wider than a roller end dimensioned to attach to the pin end of an adjacent link. It is also possible to provide a chain in which the successive links are connected by structures that are wholly different than the hollow rollers and solid pins that characterize roller chains.
The present invention provides a mechanism whereby the nature of the coupling between links in a chain can be selectively changed between rigid and relatively rotatable couplings. Along a given chain run, the couplings of the links can be made rigid for some links and rotatable for others. This opens a number of inventive possibilities that are discussed below.
However, the idea of providing a chain in which the pivot connections are switched between rigid and flexible states by means of an engaging part is known per se. In Yoshiga et al., U.S. Pat. No. 5,157,912, a connecting pin engages between otherwise-pivotable links and is laterally displaceable by external contact with a constricting structure along the chain path. The displaceable part is a spring biased lateral pin that is eccentric to the link pivot axis, and not a displaceable complementary shape. Yoshiga teaches this locking function in connection with a push-pull chain, for holding constant the length of the chain. The implication appears to be that if the joints were free, the chain would shorten when pushed (longitudinally compressed), due to pivoting of the links at their joints. Yoshiga supports the chain on a track and does not teach the possibility of making a chain self supporting against sagging and potentially variable in length.
Snapp, Jr., U.S. Pat. No. 4,141,665, teaches a general purpose angularly lockable articulated joint. Although there is a complementary shape between adjacent linked members for fixing the joint against pivoting, the engagement and disengagement involves a longitudinal lengthening and shortening. This is structurally different than the present inventive arrangement wherein locking is accomplished by lateral displacement of complementary shapes.
U.S. Pat. Nos. 4,658,577—Klein, 5,108,350—Szpakowski, 5,970,701—Roden et al. and 6,016,844—Takahashi et al. teach limits on the angle to which chain joints are permitted to pivot, in one direction. Such a chain structure is sometimes called a “Woods chain.” The disclosures of these patents concern a number of situations in which it is desirable to have a self-supporting chain. However, they fail to teach or suggest an arrangement similar to that discussed herein. Some other references in the general background are U.S. Pat. Nos. 4,635,438—Rottinghaus, 4,885,907—Pappanikolaou and 5,107,672—Featherstone. All the foregoing patents are hereby incorporated in their entireties.